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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function foo(n){
            if(n%2 == 0){
                var a =0;
                for(var i=1;i <=n;i++){
                    if(i%2 == 0){
                        a += 1/i;
                    }
                }
                return a;
            } else{
                var b =0;
                for(var i=1;i <=n;i++){
                    if(i%2 !== 0){
                        b += 1/i;
                    }
                }
                return b;
            }
        }
        console.log(foo(4));
    </script>
</body>
</html>